According to a recent report published by the United Nations Food and Agriculture Organization, the livestock is found to be a major threat to environment, as the sector is responsible for 18% green house gas emissions. The livestock sector emits 37% of anthropogenic methane that has 23 times more global warming potential than CO2 (1). Cattle and other ruminant animals produce methane in normal fermentation process, when microorganisms in their stomach break down fibers in grasses and grains they eat. The microorganisms that produce methane in ruminant fermentation are a distinct group of Methanogenic bacteria, called methanogens (2-4). An estimated 12-30% of total atmospheric methane is produced by ruminants (5). Besides having a significant impact on global warming, methane formation also represents up to 15% loss of dietary energy to the ruminant (6). Therefore, there is an urgent need to develop strategies to curtail ruminal methane emissions and improve animal performance, which will have both ecological impact as well as economic benefit.
Several strategies including chemical suppression and biotechnological interventions have been investigated to attenuate methane production and improve feed efficiency (7-9). However, there is growing concern over the use of chemical inhibitors in animals used for human consumptions, and possibility in developing chemical resistant methanogens, researchers are now focusing on developing biological strategies to solve the problem (10). Recently, it was reported that immunization of sheep with a methanogen vaccine demonstrated a minor reduction (7.7%) of methane emissions (11).
For targeting microorganisms, our laboratories have been developing passive antibody therapy approach using avian antibody technology to control gastrointestinal disease and to improve the growth performance. In earlier studies, we have shown that avian antibodies targeted to E. coli 0157:H7 were capable of reducing the shedding of E. coli 0157:H7 from sheep (13). Also, the avian antibodies targeted to the virulent factors of E. coli 0157:H7 were shown to inhibit attachment of E. coli 0157:H7 to the host cells and to block colonization of E. coli 0157:H7 (14), Furthermore, avian antibodies targeted to E. coli K-88, were demonstrated to inhibit proliferation of E. coli K-88, to block adherence to the host cells and confer protection to piglets experimentally challenged with ETEC K-88 (15). A number of researchers also have shown that IgY antibodies can be used for passive immunization or treatment of animals suffering from various bacterial and viral diseases (18-21). Furthermore, the yolk of eggs from laying hens immunized with the target antigen is shown to be an inexpensive and convenient source for polyclonal antibodies. Chickens produce three principal immunoglobulin (Ig) classes, IgM, IgA and IgG, and the functional homologue of mammalian IgG is IgY (16, 17). However, there has been no report to date on the generation of avian antibodies against methanogens and their effect on reduction of methane production. Therefore, the aim of this study was two-fold, to generate strong avian antibodies targeted to a group of the three predominant methanogens of ruminant fluid and to investigate the role of avian antibodies directed against the methanogens on ruminant methane production in vitro.